This invention relates to an isolation valve for a brake system for trains which minimizes the loss of hydraulic brake fluid upon brake line rupture.
In train brake systems a rupture or break in a brake line causes a loss of hydraulic fluid out of the system onto the track area. This spewing of brake fluid into the environment is a safety hazard, from not only a viewpoint of smell, water and ground pollution, but also fire hazards. Where third rail electric systems come into contact with the leaking fluid, there is a possibility of a fire which could set trains aflame and could cause smoke in train tunnels which could become a safety hazard to train riders waiting in stations or to riders in the train cars themselves.
It is an object of this invention to provide a simple inexpensive safety control system which will shut off the flow of hydraulic fluid to a ruptured or broken brake line.
In particular a spring based spool valve is provided which is also responsive to the force of hydraulic pressure fed to each brake actuator. Upon rupture of the brake line, the pressure of the fluid operating on the spool valve drops causing the spool valve to move to a position where it shuts off the flow of hydraulic fluid to the ruptured brake line.
The spool valve is formed by a spool having a metal stainless steel valving surfaces at each end. The spool is slidable in a housing having two inlet means leading axially into a valving chamber controlled by the valving surface from a source of hydraulic pressure and two outlet means leading to at least two sets of brake actuators. The stainless steel valving surfaces act co-jointly against spring biased stainless steel valve seats to control the flow of fluid from the inlets to the outlets in a positive manner and insure complete shutting off of the flow due to the metal to metal contact between valve surface and seat. The spool valve is spring biased to a central position by two strong spring acting on each end thereof, whereupon both inlets are normally open. The pressure in the outlet lines also acts on the spool valve, with the pressure in each line acting in opposition to one of the two bias springs. When a rupture occurs in one outlet line, the pressure therein drops an amount sufficient to cause the opposing spring and pressure in the other line to slide the spool valve to shut off the inlet line leading to the affected outlet line. Minor variations in pressure are unable to overcome the neutral positioning by the springs.
By having an axial inlet flow to the valve chamber, an improved result is obtained over a side ported inlet. The side ported inlet increases eddy currents from the incoming fluid flow requiring a stronger spring, which strong spring unduly limits the range of pressure which would cause the spool valve to limit flow to the ruptured line. Thus, by use of an axial inlet a greater operational range is obtained so that the valve can assume one of three positions (center, far left or far right) without acting as a proportional valve.
The inlet lines lead from a hydraulic power and control unit (HPCU) to both ends of the spool valve and from there pass through a spring biased valve seats into two chambers containing the spool valve and the bias springs. From each chamber the fluid flows to an outlet line for one set of brake actuators. Outboard of the valve seats are valve seal retainer plugs which can be unscrewed to allow for replacement of any of the valve seats, bias springs, and the valve spool valve.
The brakes are spring actuated and pressure released. The HPCU control unit includes a pressure limit control so that a maximum pressure in the system is not exceeded.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing.